In multiple-cylinder two stroke internal combustion engines, especially in the type used for marine outboard engines, it is common for two cylinders to be side by side (juxtaposed). The exhaust passage from one cylinder passes near the other, and tends to overheat a localized portion of the other cylinder. The resulting out-of-roundness causes loss of power by blow-by, and accelerated wear. It is an object of this invention to overcome this problem.